Visual and Non-Visual Navigation in Blind Patients with a Retinal Prosthesis.

Garcia S, Petrini K, Rubin GS, Da Cruz L, Nardini M - PLoS ONE (2015)

Bottom Line:
Participants completed a path reproduction and a triangle completion navigation task, using either an indirect visual landmark and non-visual self-motion cues or non-visual self-motion cues only.In both tasks, control participants showed better precision when navigating with reduced vision, compared to without vision.Additionally, all patients showed greater precision than controls in both tasks when navigating without vision.

Affiliation: Institute of Ophthalmology, University College London (UCL), London, United Kingdom.

ABSTRACTHuman adults with normal vision can combine visual landmark and non-visual self-motion cues to improve their navigational precision. Here we asked whether blind individuals treated with a retinal prosthesis could also benefit from using the resultant new visual signal together with non-visual information when navigating. Four patients (blind for 15-52 years) implanted with the Argus II retinal prosthesis (Second Sight Medical Products Inc. Sylmar, CA), and five age-matched and six younger controls, participated. Participants completed a path reproduction and a triangle completion navigation task, using either an indirect visual landmark and non-visual self-motion cues or non-visual self-motion cues only. Control participants wore goggles that approximated the field of view and the resolution of the Argus II prosthesis. In both tasks, control participants showed better precision when navigating with reduced vision, compared to without vision. Patients, however, did not show similar improvements when navigating with the prosthesis in the path reproduction task, but two patients did show improvements in the triangle completion task. Additionally, all patients showed greater precision than controls in both tasks when navigating without vision. These results indicate that the Argus II retinal prosthesis may not provide sufficiently reliable visual information to improve the precision of patients on tasks, for which they have learnt to rely on non-visual senses.

pone.0134369.g003: Graph showing improvement in variable error (A) or constant error (B) when using vision against errors when navigating without vision.Shading indicates the 95% confidence intervals computed from the control data. Path Reproduction: Patients did not show similar improvements in precision or accuracy when navigating with the prosthesis as controls. All had lower variable errors without vision, and three had lower constant errors without vision, compared to controls. Triangle Completion: Two of four patients showed similar improvements in precision when using vision as controls, and all patients showed lower variable errors without vision compared to controls. Two patients had lower constant errors without vision compared to controls.

Mentions:
A paired samples t-test indicated that control participants had significantly higher variable errors without vision than with vision (t[10] = 3.806, p = 0.003). Based on these control data, 95% of normally sighted participants would be expected to show reductions in error of 0.105m–0.402m. Patient data fell outside of these confidence intervals, and three of four showed better performance without vision. In addition, all four patients’ variable errors without vision were less than the lower limit of the 95% confidence intervals of normally sighted participants (ID 001–004: 0.115m, 0.031m, 0.084m, 0.117m compared to 95% CI: 0.178m–0.483m; see Fig 3A).

pone.0134369.g003: Graph showing improvement in variable error (A) or constant error (B) when using vision against errors when navigating without vision.Shading indicates the 95% confidence intervals computed from the control data. Path Reproduction: Patients did not show similar improvements in precision or accuracy when navigating with the prosthesis as controls. All had lower variable errors without vision, and three had lower constant errors without vision, compared to controls. Triangle Completion: Two of four patients showed similar improvements in precision when using vision as controls, and all patients showed lower variable errors without vision compared to controls. Two patients had lower constant errors without vision compared to controls.

Mentions:
A paired samples t-test indicated that control participants had significantly higher variable errors without vision than with vision (t[10] = 3.806, p = 0.003). Based on these control data, 95% of normally sighted participants would be expected to show reductions in error of 0.105m–0.402m. Patient data fell outside of these confidence intervals, and three of four showed better performance without vision. In addition, all four patients’ variable errors without vision were less than the lower limit of the 95% confidence intervals of normally sighted participants (ID 001–004: 0.115m, 0.031m, 0.084m, 0.117m compared to 95% CI: 0.178m–0.483m; see Fig 3A).

Bottom Line:
Participants completed a path reproduction and a triangle completion navigation task, using either an indirect visual landmark and non-visual self-motion cues or non-visual self-motion cues only.In both tasks, control participants showed better precision when navigating with reduced vision, compared to without vision.Additionally, all patients showed greater precision than controls in both tasks when navigating without vision.

Affiliation:
Institute of Ophthalmology, University College London (UCL), London, United Kingdom.

ABSTRACTHuman adults with normal vision can combine visual landmark and non-visual self-motion cues to improve their navigational precision. Here we asked whether blind individuals treated with a retinal prosthesis could also benefit from using the resultant new visual signal together with non-visual information when navigating. Four patients (blind for 15-52 years) implanted with the Argus II retinal prosthesis (Second Sight Medical Products Inc. Sylmar, CA), and five age-matched and six younger controls, participated. Participants completed a path reproduction and a triangle completion navigation task, using either an indirect visual landmark and non-visual self-motion cues or non-visual self-motion cues only. Control participants wore goggles that approximated the field of view and the resolution of the Argus II prosthesis. In both tasks, control participants showed better precision when navigating with reduced vision, compared to without vision. Patients, however, did not show similar improvements when navigating with the prosthesis in the path reproduction task, but two patients did show improvements in the triangle completion task. Additionally, all patients showed greater precision than controls in both tasks when navigating without vision. These results indicate that the Argus II retinal prosthesis may not provide sufficiently reliable visual information to improve the precision of patients on tasks, for which they have learnt to rely on non-visual senses.